2 THE LIVING PLANT 



and in this swelling a relatively great force is exerted : Stephen 

 Hales in his classical experiment found that the force exerted 

 by swelling peas was sufficient to raise a weight of 184 

 pounds.* 



The second phase in germination is now initiated, growth 

 starts : but growth is impossible without food to supply the 

 wherewithal for new structures and to make good the waste, 

 for vital activity requires energy which is obtained by various 

 oxidative processes. Thus aerobic respiration, the ordinary 

 catabolic process of green plants, is a marked feature con- 

 current with growth and may be sufficiently intense to cause 

 an obvious rise in temperature. The required food, chiefly 

 fats, carbohydrates and proteins, are stored in the embryo 

 itself or in special tissues, endosperm and perisperm : and 

 since the food is stored in a form mostly insoluble and 

 non-assimilable, water is the first essential and appropriate 

 enzymes the second, for not before it is hydrolized can food 

 be translocated from its storage cells and passed by osmotic 

 processes to the active tissues. The enzymes may be 

 elaborated in the cells or tissues containing the food, or 

 may be secreted by specialized structures, the scutellum for 

 example. Often the products of hydrolysis may be recognized 

 by simple means, sugar, for instance, in germinating barley. 

 In other cases their assimilation may be so rapid that 

 identification is difficult; indeed, sometimes their presence 

 can only be inferred from the results of carefully-controlled 

 test-tube experiments, glycerol, for example, in germinating 

 Ricinus. The embryo thus presented with appropriate food, 

 grows and develops. Growth is to a certain degree an 

 understandable problem which, on the present elementary 

 occasion, can be sufficiently indicated in a few words. Of 

 necessity must a cell be nourished through its surface and 

 growth will take place if assimilation be greater than waste 

 by oxidative and kindred processes. But growth means 

 increase, and as this increase in bulk takes place the surface 

 area of the cell is proportionally lessened. A stage ultimately 

 will be reached when the area of the surface is so limited 

 in proportion to the volume of the cell as to permit the 

 entry of only sufficient food to make good the losses ; thus 



* Hales: "Vegetable Staticks," 3rd Edition, London, 1738, p. 102. 



